1. Field of the Invention
The present invention relates to a signal detecting device and a signal detecting method for detecting a signal recorded on a recording medium using near-field light.
2. Description of the Related Art
A light recording and reproducing method employing near-field light attracts attention as a technique for realizing an ultra-high density storage because the technique can realize high resolution regarded as a limit of a normal optical system. For example, when a so-called near-field light lens such as a solid immersion lens (SIL) is used, it is considered possible to reduce a spot diameter up to about 100 nm.
It is expected that surface recording density 1 Tbit/inch2 will be realized in a hard disk around the year of 2012. However, to realize recording density equivalent to the surface recording density, it is necessary to set a spot diameter to be equal to or smaller than 20 nm.
Therefore, in order to reduce further reduction in the spot diameter, researches and developments making use of local light spot formation by the plasmon resonance phenomenon are actively performed. It is expected that the density of a phase change optical recording system is increased by applying the local light spot to a phase change medium.
On the other hand, it is considered difficult to reproduce ultra-high density recorded information using near-field light because it is difficult to directly observe the near-field light.
As measures against this difficulty, there is proposed a method of irradiating observation light on a sample and irradiating reference light on a cantilever arranged in a position different from a signal detection position of the sample or near the sample, comparing the reference light and the observation light, and detecting near-field light according to a phase difference between the reference light and the observation light (see F. Zenhausern, et al. “Apertureless near-field optical microscope”, Appl. Aphys. Lett., 65(13), 1994 (Non-Patent Document 1) and Y. Martin, et al. “Optical data storage read out at 256 Gbits/in.2”, Appl. Phys. Lett., 71(1), 1997 (Non-Patent Document 2)).
There is also proposed a technique for providing a scatterer shot-key joined on a semiconductor substrate, causing surface plasmon and exciting a carrier in the semiconductor substrate to thereby use the scatterer as a near-field probe (see JP-A-2002-368253).